Microwire Composites Research Articles

Responsive left-handed behaviour of ferromagnetic microwire composites by in-situ electric and magnetic fields

Ferromagnetic microwires are feasible building blocks for the construction of electromagnetic composites with tunable left-handed response towards external stimulus. In this work, a typical left-handed signature of the transmission window was revealed in Co-rich microwires ranging from 9.3 to 10.4 GHz, which arised from the ferromagnetic resonance under a constant DC magnetic field of 8 Oe. Such window was modulated by applying a DC current which tended to compensate the magnetic anisotropy of the microwires. Currents of up to 100 mA were applied to the wire resulting in a maximum transmission bandwidth at 60 mA. Such effect was corroborated by the competition between magnetic domains restoration and Joule effect in the presence of DC current. Embedding the microwire into fibre-reinforced 913 E-glass prepregs realised a metacomposite with a corresponding window in 8.5–10.2 GHz benefited by the restoration of circumferential domain structures during the composite curing process. Further, it was observed a dependence of electromagnetic behaviour on the angle between the microwire and the reinforcing glass fibers of the matrix. This investigation provides essential guidance for designing and tuning frequency-selective wave transmitting structures for potential sensing and cloaking applications.

Programmable microwire composites: from functional units to material design

Microwire composites possess a wide range of functionalities that can be actively manipulated by magnetic field/stress stimuli or hybridization. Beyond those strategies, here we focus on programming microwave response by designing the wire functional units and assembling them in a specific arrangement. The programming was based on a code type defined by structural relaxation and electromagnetic damping and on a code pattern by wave attenuation, effective conductivity and near-field interaction effects. Structural relaxation was achieved by current annealing the wires, which was reflected in changes in Curie temperature, structural, magnetic and electrical properties. The wave propagation mapped by the transmission coefficient was manipulated by the wire concentration and periodicity and by arrangement of as-cast and annealed wires in their array. Increasing the wire concentration blueshifted the transmission band of the wire composites due to larger conductivity, while decreasing the wire periodicity redshifted the band owing to stronger inter-wire coupling. A larger blueshift was obtained by alternating as-cast and annealed wires due to an overlapped flow closure of fields from the same type of wire in the array. Our strategy demonstrates that macroscopic properties of wire composites can be effectively programmed from a material structure/unit arrangement perspective. This concept promotes deeper understanding of high-frequency properties and further expands the applications of fiber-reinforced composites in fields such as information, energy and security technologies.

Effect of Microwire Alloy Composition, Orientation, and Content on the Microwave Properties of Glass-coated Alloy Microwire Composites

The microwave properties of microwire alloy composition, the orientation of microwires, and the content of glass-coated FeCuNbVSiB, FeSiBCMn, and CoFeNiSiB microwire composites were studied. The transmission/reflection (T/R) coaxial line method was used to measure the relative complex permeability and complex permittivity for the microwire/rubber composites. The measured results show that the microwave permeability of randomly oriented glass-coated microwires is the highest, while that of the radially oriented glass-coated microwires is the lowest for different microwires orientation. The resonance frequency of the FeSiBCMn microwires and the permeability of the CoFeNiSiB microwires are the highest for different microwire alloy composition. The microwave permittivity of radially oriented glass-coated microwires is the strongest, the axially oriented glass-coated microwires is the lowest for different microwires orientation. The permittivity of the FeCuNbVSiB microwires is the highest for different microwire alloy composition.

Microwave absorbing properties of composites containing ultra-low loading of optimized microwires

A set of composite absorbers with ultra-low loading of down to 0.017 wt.% short-cut microwires were prepared and investigated in terms of their magnetic and microwave properties in the X-band (8–12 GHz). The key parameters that could factor into the performance of the present absorbers have been systematically studied from micro to macro scale, i.e., the magnetic domain structure modulated by different internal stress scenarios, microwire aspect and composite filling ratio, and relative importance of impedance matching and material loss. Longer wires (9 mm) and wires after suitable treatment lead to the enhancement of microwave absorbing property mainly due to the larger magnetic loss resulted from the natural ferromagnetic resonance, which is induced in the domain rotation and reversal process. The internal stress modification by removal of glass and joule annealing has profound effects in formulating the microwave absorption frequency and intensity of microwire composites by tailoring the domain structure and local anisotropy field. It is found that the composites with microwires annealed at 132 mA for 15 min obtain the minimum reflection loss and broadest absorption bandwidth with reference to −10 dB at 1.5 mm thickness, which is −25.7 dB (0.81 GHz) at 11.39 GHz caused by the relative high attenuation constant and best matching condition where Zreal is 1.026 and Zimag is −0.102. This indicates that impedance matching plays a dominant role in tailoring the microwave absorbing property. Remarkably, the unconventional absorption frequency - matching thickness relation based on the quarter-wavelength model offers possibility to address the limitation of thickness for low frequency absorbing application.

Synthesis and magnetic properties of Ta/NdFeB-based composite microwires

Magnetic NdFeB-based microwire composites have been prepared by the direct current magnetron sputtering technique in a specifically designed sputtering chamber for thin-film deposition in wire geometry. As substrate wire material, we have employed steel and Ta. Annealing of the substrate wires during the deposition process was performed by ohmic heating through the application of a direct current. Samples were characterized by means of vibrating sample magnetometry (VSM) and scanning electron microscopy. Best properties have been encountered when using Ta wires as core (substrate) material. The VSM data show a dramatic impact of the current applied during the deposition process on the magnetic properties. For higher current values, i.e., higher annealing temperatures, the wires exhibit a reversal process that is typical for a two-phase system. Moreover, an increase of the coercive field (and remanent magnetization) is observed, which is ascribed to a modification of the magnetic phase present in the sample due to the annealing. We find an indication for the formation of a magnetic easy-axis direction which is azimuthally oriented around the wire axis.

In-situ microwave characterization of ferromagnetic microwires-filled polymer composites: A mini review

This review describes the emerging res earch area and relevant physics of polymer-based composites enabled by amorphous ferromagnetic microwires. Fruitful results ranging from their tunable magnetic field and mechanical stress properties and influences of direct current on their microwave behavior are displayed in addition to the brief analysis on the underlying physics. The multifunctionalities exhibited strongly imply a variety of potential applications such as structural health monitoring and high-performance sensors. This article underlines that the future challenge mainly lies in proper microwire tailoring in expectation of a better microwave performance of microwire composites.

Metacomposite characteristics and their influential factors of polymer composites containing orthogonal ferromagnetic microwire arrays

The microwave properties of glass-fibers reinforced polymer composite embedded with an orthogonal array of Fe77Si10B10C3 microwires have been investigated. The composites containing orthogonal wire arrays display a remarkable transmission window in the frequency band of 1 to 6 GHz under zero external magnetic field indicating an intrinsic double-negative-index characteristic. The polymer matrices have proved to exert a synergistic effect on the microwave properties, which is responsible for the disappearance of the transmission windows when Ek is perpendicular to the glass fiber direction. The plasma frequency of the orthogonal microwire array composite is higher than that of the parallel microwire array with identical wire spacing; this could be attributed to the enhanced microwire-wave interaction induced by the axial electrical components on the additional layer of perpendicular wires. All these features make this new kind of orthogonal microwire composites promising for potential cloaking and sensing applications.

Lateral charge propagation effects during the galvanic replacement of electrodeposited MTCNQ (M = Cu, Ag) microstructures with gold and its influence on catalyzed electron transfer reactions

The galvanic replacement of isolated electrodeposited semiconducting CuTCNQ microstructures on a glassy carbon (GC) substrate with gold is investigated. It is found that anisotropic metal nanoparticles are formed which are not solely confined to the redox active sites on the semiconducting materials but are also observed on the GC substrate which occurs via a lateral charge propagation mechanism. We also demonstrate that this galvanic replacement approach can be used for the formation of isolated AgTCNQ/Au microwire composites which occurs via an analogous mechanism. The resultant MTCNQ/Au (M=Cu, Ag) composite materials are characterized by Raman, spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and investigated for their catalytic properties for the reduction of ferricyanide ions with thiosulphate ions in aqueous solution. Significantly it is demonstrated that gold loading, nanoparticle shape and in particular the MTCNQ–Au interface are important factors that influence the reaction rate. It is shown that there is a synergistic effect at the CuTCNQ/Au composite when compared to AgTCNQ/Au at similar gold loadings.

Tunable properties of microwire composites at microwave frequency

Tunable electromagnetic properties (permeability and permittivity) of composites filled with glass-coated microwires under external magnetic field were investigated experimentally. The microwire composites have been measured with 7 mm coaxial airline fixture and vector network analyzer from 0.01 to 18 GHz. The ferromagnetic resonance may contribute to the tunability of permeability of microwire composites. The tunability of effective dielectric permittivity may be attributed to the magneto-impedance effect. The microwire composites are promising candidates for smart or tunable applications at microwave frequency.

In situ microwave characterization of microwire composites with external magnetic field

Rubber composites containing Co68.15Fe4.35Si12.25B15.25 glass-covered amorphous microwires were fabricated. For samples containing 5 mm long wires and randomly dispersed in the polymer matrix, our results demonstrate that the current induces resonance of circumferential permeability (magnetoimpedance resonance) resulting in a significant change of the effective permittivity of the wire-filled composites with application of a high magnetic field. For samples containing longer wires (70 mm) periodically arranged in the polymer matrix, the permittivity spectrum shows two resonance peaks due to, respectively, dipole and magnetoimpedance resonance. The induced magnetoimpedance resonance has a narrower linewidth than the dipole one as magnetic field is increased.

Effects of wire properties on the field-tunable behaviour of continuous-microwire composites

The microwire composites consisting of continuous Co-rich amorphous glass-coated ferromagnetic microwires embedded in a E-glass prepreg matrix were fabricated, and the influences of wire periodicity (b), composition and radius on the field-tunable properties have been systematically investigated in a broad microwave frequency range of 0.9–18GHz. It has been found that the field tunability, effective operational frequency and field of the composites are strongly dependent on these factors. With decreasing b from 15 to 7mm, the field tunability of effective permittivity (nɛ) increases from 0.77% to 16%m/A by more than 20 times. The detected cups and resonances of the transmission and reflection spectra are identified. Their changes with wire periodicity have been shown to be due to a combination of the dielectric and magnetic response arising from the interactions between microwave and microwires and microwires by themselves. The best possible field tunability occurs below the plasma frequency. The effective magnetic field for realisation of the field-tunable properties has been found to be about 500A/m, which is associated with the anisotropy field. In addition, field tunability is found to be positively correlated with the magnetic softness and GMI properties of the wire fillers, which are determined by the wire composition and geometry. These findings are of practical importance in developing multifunctional microwire composites for a broad range of engineering applications, such as structural health monitoring, NDT and microwave tunable devices.

In situ microwave characterization of microwire composites under mechanical stress

We present results of an experimental characterization of the dielectric properties and microwave absorption of rubber composite samples containing Fe4Co68.7Ni1B13Si11Mo2.3 amorphous microwires which are submitted to a low uniaxial tension. Measurements of the dielectric loss and microwave absorption as a function of strain over the frequency range of 300 MHz-6 GHz reveal that the uniaxial elongation randomly breaks wires at about 2.8% strain and this has for effect to decrease the loss factor for larger strain. Two possible mechanisms are identified to account for our observations, namely, the stress and shape effects. The ability to control this stretch breaking phenomenon will be instrumental to developing stress tunable microwire composites for sensing applications.

Giant magneto-impedance and stress-impedance effects of microwire composites for sensing applications

Composites consisting of glass-coated amorphous microwire Co 68.59Fe 4.84Si 12.41B 14.16 and 913 E-glass prepregs were designed and fabricated. The influences of tensile stress, annealing and number of composite layers on the giant magneto-impedance (GMI) and giant stress-impedance (GSI) effects in these composites were investigated systematically. It was found that the application of tensile stress along the microwire axis or an increase in the number of composite layers reduced the GMI effect and increased the circular anisotropy field, while the annealing treatment had a reverse effect. The value of matrix–wire interfacial stress calculated via the GMI profiles coincided with the value of the applied effective tensile stress to yield similar GMI profiles. Enhancement of the GSI effect was achieved in the composites relative to their single microwire inclusion. These findings are important for the development of functional microwire-based composites for magnetic- and stress-sensing applications. They also open up a new route for probing the interfacial stress in fibre-reinforced polymer (FRP) composites.

Mechanical–electromagnetic coupling of microwire polymer composites at microwave frequencies

We have fabricated a set of microwire composites with varying wire concentrations and studied their effective complex permittivity under the tensile stress at a frequency range of 1–6 GHz. It has been found that with increasing wire concentration the composite presents increasing effective permittivity and strain sensitivity. The Gaussian molecular network model shows a complex strain dependence of sensitivity due to the composite architecture influenced by the wire concentrations. All these results indicate the proposed composite are excellent candidate materials for the microwave sensing and structural interrogation applications.